Apparatus for use in treatment of photoengraving plates, and photolithographic plates



Sept. 23, 1941. J A. CHR|STMAN 2,256,825 APPARATUS FOR USE IN TREATMENT OF PHOTOENGRAVING PLATES,

AND PHOTOLITHOGRAPHIC PLATES Filed May 25, 1940 ,jgwl.

g l6 I4 INVENTOR Patented Sept. 23,1941

UNlTED stares; Parent orrics APPARATUS FOR USE IN TREATMENT OF PHOTOENGRAVING PLATES, AND PHOTO- LITHOGRAPHIC PLATES Joseph A. Christman, Pittsburgh, Pa.

Application May 23, 1940, Serial No. 336,776 6 Claims. (01. 91 42) My invention relates to photolithographicor photoengraving plates, and consists in apparatus for use in preparing the plates for service.

A plate of the sort with which my invention is particularly, if not exclusively, concerned consists in a thin sheet of metal, ordinarily aluminum, or zinc, or copper, in the order of from .001" to .005" in thickness. (Probably such plates or sheets should be termed metal foil, but I shall use the given terms, inasmuch as the invention undoubtedly will find utility in the treatment of photolithographic and photoengraving elements of thicker and more rigid structure, that more accurately fall within the term plates.)

In the preparation of such a plate for service, a sensitizing solution--a known liquid composition including certain actinic ingredients-is applied, cured and dried on one surface of the plate. Not only must the sensitizing solution be distributed with absoluteuniformity, but it must be dried and baked with heat of precisely determined concentration, a concentration that is uniformly effective, and preferably intermittently-applied, over the entire expanse of the plate body. The achievement of this thing, with oertainty in every case, has long presented a problem to the art, and hitherto the perfect solution of the problem has not been realized, notwithstanding the fact that many and various apparatus for the purpose have been developed. Such being the situation, it is to be understood that my invention consists in an improved apparatus that will do the job adequately and with substantial perfection.

An apparatus or machine embodying the invention is shown in the accompanying drawing. Fig. I is a view of the machine in side elevation, and Fig. II is a view thereof in plan from above. Fig. III is a diagrammatic view of the electrically driven mechanism that propels the moving uarts of the machine. Fig. IV is an electrical wiring diagram.

Referring to the drawing, the machine includes a frame or base I, upon which is borne a device 2 for the support of a plate undergoing treatment, and a heating unit 3 for drying and curing the sensitizing solution applied in accordance with known procedure to such plate. The plate-supporting device consists in a horizontal platform mounted for rotation upon the upper end of a vertical spindle 4, while the heating unit, consisting in an electrical plate of known sort, is mounted in a plane parallel to, and arlutions per minute, and the heating unit 3 is oscillated beneath the support, between the broken and full-line positions, Fig. II, at about thirty.- five oscillations per minute.

The mechanism for oscillating the heating unit includes a crank 6, and a link I interconnecting the distal end of such crank with the body of the heating unit, as at 8, at an interval from the eccentric axis 5 on which the unit is adapted to be oscillated. Advantageously, with synchronism of motion of plate support .2 and heating unit 3 in '1 mind, the crank 6 is driven by one and the same ranged at an interval below, the planeof the electric motor 9 as drives the spindle t. Through a suitable trainof gears Ii], Fig. III, the motor 9 (a motor characterized as a low-speed motor) is connected to drive the Vertical spindle 4 that carries the plate support 2, and through gears H the train of gears It] is adapted to drive a spindle I2 upon which the crank 6 is secured. The gearing is so designed and arranged as toaiford the desired speed of rotation of the plate support 2 relatively to the heating unit 3, and the desired speed of oscillation of the heating unit relatively to the plate support. The base I of the machine is recessed beneath, to receive in compact assembly the motor 9 and the gearing it], II, the gearing being housed, if desired, within a gear-box [3, Fig. I.

Connectionof the motor 9, and of the resistor element 30 (Fig. IV) of the heating unit 3, to a source of electric energy is made With the conventional plug-in cord M, and it is important to note that the energizing of the motor is adapted to be effected independently of the resistor element of the heating unit. The energizing of the motor is controlled by means of a push-button switch [5, and the energizing of the resistor element of the heating unit by means of a switch l6, as indicated diagrammatically in Fig. IV. Thus, for reasons presently to appear, the plate support 2 can be set in rotation at desired time interval before the resistor element of the heating unit is energized. The connections between the resistor element of the heating unit and the switch It include a flexible cable 3! (Fig. I), whereby accommodation is made for the essential relative movement between the heating unit and the base I. I

In the use of the machine a photoengraving plate is laid infiat position upon the horizontal surface of the support 2, and a charge of sensitizing solution is applied to the upper surface of the plate. Then the switch 15 is closed, with the effect that the motor 9 is energized and the supported plate set in rotation, it being noted in passing that the heating unit 3, with its resistor element 30 not yet energized, oscillates idly beneath the whirling or rotating plate. Under the influence of a slight but sufficient centrifugal force, the liquid solution on the slowly rotated plate tends to flow outward upon the surface of the plate; excess solution is thrown outward from the rim of the plate, and that remaining on the plate is distributed in uniform thickness over its entire upper surface. One hundred and fifty rotations of the plate at fifty R. P. M. (or three minutes of operation of the machine) is adequate in the usual case to gain the desired distribution of solution. Then, the switch I6 is closed and the oscillating unit 3 caused to generate the heat required to effect the essential baking and curing of the uniformly applied solution, and the application of heat is continued until the solution is hardened and dried.

The accomplishment of the desired baking and drying of the solution uniformly over the entire coated surface of the plate is the thing that has been difficult. The heat of the incandescent filament or resistor 30 is applied by convection and radiation to the bottom of the rotating plate; the heat must be a moderate heat, such as is realized by maintaining the plate at an interval above the incandescent filament of the heating unit; and the heat must be uniformly applied, and preferably intermittently applied over the entire nether surface of the plate. With these comments in mind, the value of the structural refinements of my apparatus may be more readily brought into focus.

First it is to be noted that the heating unit is oscillated through a range (cf. broken and fullline positions, Fig. II) that is effective through the entire radial extent of the support 2 and the photoengraving plate carried thereon; that is, through the greatest extent, as well as the least, of the periphery of the rectangular plate from the center (4) of plate rotation. Thus, with the support in rotation and the heating unit in continuous oscillation, the heat rising from the unit is effective on successive areas of the plate intermittently, permitting no area to become overheated and no area to be underheated. Indeed, the crank mechanism 6, l operates to oscillate the heating unit, in its range of movement about axis 5, with a varied rather than a constant angular velocity, and it has been found that this factor contributes to the good results experienced.

Turning to the structure of the plate support itself, several important details of construction are to be noted. The plate support consists in a rectangular expanse of fine screen 20 (fragmentarily indicated in Fig. II), through the interstices of which the entire bottom surface of the supported plate is exposed to the heat of unit 3. The screen 26, a screen of fine metal wire, is drawn taut and marginally secured, as by Welding or soldering, to a frame 2| of small metal rod of from to A in diameter. The open-work screen 20 provides the immediate support for the photoengraving plate (not shown) to be treated, and the screen 20 and its frame are in turn supported by means of four radial arms 22. The arms are anchored at their outer ends to the frame 2|, with their tips extended above the face of screen 20 to provide lateral stays for the plate upon the screen; from the points of integration with frame 2| the arms extend first downward and then inward, beneath the plane of the screen, and at their inner ends the arms are secured to a socket member 23 removably secured upon the upper end of spindle 4. The arms 22, as in the case of the frame 2|, are formed of metal rod of small cross section, and it is important to note (Fig. I) that such arms are spaced at a substantial interval below the plate-supporting screen 20, for by virtue of such organization, the heat generated by the oscillating heating unit has full access to the nether surface of the plate-supporting screen 20, to substantially the same extent as it would if the screen were freely floating in the air above the heating unit. This feature, together with that of forming the frame 2| and arms 22 of minimized cross section and mass, is important to insure that photoengraving plate borne by the screen will be subject over all its area to an uniform heating effect of the unit 3 beneath. There is no massive element adjacent .to the supported plate to absorb heat, nor to interfere with the radiation and convection of heat from the unit 3 to the plate undergoing treatment. Such is the structure of the apparatus that has met a definite need in the art.

I claim as my invention:

1. A machine for curing and drying photoengraved plates that comprises a plate-supporting device and a heating unit mounted in spacedapart relation, means for rotating said supporting device relatively to the heating unit, means for oscillating the heating unit relatively to said supporting device, and means for manually controlling the rotation of the device-rotating means and the heating effect of said unit severally, with the effect that heat may be brought to play upon a supported plate at desired sequence with respect to the time of initiation of plate rotation.

2. A machine for curing and drying photoengraved plates that comprises a machine frame carrying a plate-supporting device and a heating unit in spaced apart relation, with the supporting device mounted for rotation relatively to the heating unit and the heating unit mounted for oscillation relatively to the supporting device, mechanism including an electric motor for effecting the relative rotation of the supporting device with respect to the heating unit and the oscillation of the heating unit with respect to the supporting device, means for manually controlling the operation of such mechanism, and means for manually controlling the heating effect of such unit, with the effect that the heat of the unit may be rendered effective in desired timed relation with respect to initiation of platesupporting-device rotation.

3. A machine for curing and drying photo engraved plates that comprises a machine base a horizontally disposed plate-supporting device mounted for rotation on a vertical axis, a horizontally disposed electrical heating plate mounted for periodic movement, relatively to said supporting device, in a horizontal plane spaced at an interval below the supporting device, means including an electric motor for rotating such plate-supporting device relatively to said heating plate, and means connected to such motor, for effecting said periodic movement of the heating plate. 1

4. The structure of claim 3, in which said heat-1 ing plate is mounted for oscillation upon a vertical, eccentric axis; said means for effecting periodic movement of the heating plate comprising a rotating crank and a connecting rod pivotally connecting the crank to the heating plate at an interval from said eccentric axis.

5. The structure of claim 3, in which said plate-supporting device consists in a light'openwork screen sustained in flat, taut condition upon a supporting frame, rod-like sup-porting arms connecting the axis of rotation of the device to the frame at the periphery of said screen, said arms in their extent from said axis to the frame at the periphery of the screen being spaced at an interval below the screen.

6. A rotary support for photoengraving plates 7 'or sheets comprising a fine open-work screen 

